1. Field of the Invention
This invention relates to a system for and method of controlling fuel flow to a heating device, and more particularly to a system for and method of controlling fuel flow to a vertical vapor generator or vaporization tube located in a combustion chamber of a heating device of a self-generating type in a stable, readily changeable and predictable manner.
2. Description of the Prior Art
Self-generating heating devices are known in which liquid fuel is fed from a fuel supply tank to a vertical vapor generator or vaporization tube in which the liquid fuel is heated and converted to a vapor state using heat from the combustion process. The resultant fuel vapor proceeds upward through the vertical vaporization tube and then into a downwardly extending vertical vapor-conducting "down" tube from which it feeds and mixes with air in a combustion chamber of the heating device. Thus, after initial ignition in the combustion chamber, the heating device heats the vaporization tube externally to generate its own fuel vapor for continued combustion in a self-generating manner.
Typically, in feeding of the liquid fuel to the vertical vaporization tube, fuel initially flows from the supply tank by gravity to a float valve comprising an inlet valve and a float member. The liquid fuel flows through the inlet valve into the float valve under the control of the float member, with the float member closing the inlet valve when a float chamber becomes filled to a desired level, and opening the inlet valve to maintain the desired fuel level as the liquid fuel feeds out of the float chamber. The float valve is mounted in a fixed position in which the fuel level in the float valve is just below the level of an elbow-type connector member which connects the vertical vaporization tube to the vapor-conducting down tube adjacent the upper end of the vaporization tube.
Flow of the liquid fuel from the float valve is controlled by adjusting a relatively small variable opening or orifice in a metering valve, as for example, by a rotatable spool or a vertical metering stem. However, if the liquid fuel is changed from one type of fuel, having a relatively low viscosity, such as gasoline, to a fuel having a higher viscosity, such as diesel fuel, the fuel flow through the metering valve will be less for a given setting and temperature, requiring a change in the setting of the metering valve control orifice for delivery of the same amount of fuel. Similarly, changes in temperature also require different fuel flow settings of the fuel metering valve control orifice, and foreign particles or sediment in the fuel can adversely affect the rate of fuel flow through the small metering valve control orifice. The required manual adjustment of the metering valve control orifice also can be objectionable in certain applications because of the time involved to achieve an appropriate setting.
Further, in many heating device applications, it is desirable, and in some instances essential, that the fuel flow rate be controlled within a narrow range despite variables, such as the abovementioned viscosity and temperature. For example, a heating device that comprises a thermoelectric converter for converting heat energy into electrical energy, is such an application. In this type of heating device, the power produced by the thermoelectric converter is proportional to the fuel flow rate, and to obtain best performance from the thermoelectric converter, its hot junction electrode temperature should be as high as possible. Thus, if the fuel flow rate varies across too broad a range, as is generally the case in control systems using an orifice-varying metering system as above described, either the temperature at the hot junction electrode or electrodes of the thermoelectric converter is not high enough and the power produced by the thermoelectric converter may be too low, or the thermoelectric materials of the thermoelectric converter may be damaged by overheating.
In addition to a fuel flow control system as above described, other fuel flow control systems also are known in the art. For example, U.S. Pat. No. 2,527,921 to W. W. Every discloses a vertically adjustable float valve for varying fuel flow to an oil burner, and U.S. Pat. No. 2,548,830 to C. P. Thomas et al discloses a stove having a vertically adjustable vaporizing pot-type burner-and-control unit, with the control unit including a float valve and a stem-type metering valve. Further, examples of known heaters which employ thermoelectric converters include that disclosed in a paper No. 13 entitled "A Thermoelectric Heater for Low Temperature Operation of Military Vehicles", presented by Carmine Luciani and Thomas L. Nystrom at the International Power Source Symposium in Brighton, England, in September 1980. Another heater of this type is that disclosed in U.S. Pat. No. 4,843,273, issued June 27, 1989, to H. Dammers et al, and entitled "Heater Mechanism with Thermoelectric Power Generator".
Accordingly, a primary purpose of this invention is to provide a fuel flow control system and method in which the rate of liquid fuel flow to a vertical vaporization tube, and consumption of fuel in an associated combustion chamber of a heating device, is controlled directly by a vertically adjustable float valve without the need for a metering orifice-type valve, whereby the fuel flow rate is stable, readily changeable and predictable, despite variable parameters, such as viscosity and temperature, and the presence of foreign particles or sediment in the fuel.